Influence of Gaze Position on Grasp Parameters For Reaches to Visible and Remembered Stimuli

In order to pick up or manipulate a seen object, one must use visual signals to aim and transport the hand to the object’s location (reach), and configure the digits to the shape of the object (grasp). It has been shown that reach and grasp are controlled by separate neural pathways. In real world conditions, however, all of these signals (gaze, reach, grasp) must interact to provide accurate eye-hand coordination. The interactions between gaze, reach, and grasp parameters have not been comprehensively studied in humans. The purpose of the study was to investigate 1) the effect of gaze and target positions on grasp location, amplitude, and orientation, and 2) the influence of visual feedback of the hand and target on the final grasp components and on the spatial deviations associated with gaze direction and target position. Seven subjects reached to grasp a rectangular “virtual” target presented at three orientations, three locations, and with three gaze fixation positions during open- and closed-loop conditions. Participants showed gaze- and target-dependent deviations in grasp parameters that could not be predicted from previous studies. Our results showed that both reach- and grasp-related deviations were affected by stimulus position. The interaction effects of gaze and reach position revealed complex mechanisms, and their impacts were different in each grasp parameter. The impacts of gaze direction on grasp deviation were dependent on target position in space, especially for grasp location and amplitude. Gaze direction had little impact on grasp orientation. Visual feedback about the hand and target modulated the reach- and gaze- related impacts. The results suggest that the brain uses both control signal interactions and sensorimotor strategies to control and plan reach-and-grasp movements.